Fast transient response for switching regulators

ABSTRACT

The present disclosure describes apparatuses and techniques of fast transient response for switching power regulators. In some aspects, a detection is made of a switching regulator&#39;s transition to a continuous mode of operation to provide current to a load. In response to the transition, a predefined current limit of the switching regulator&#39;s current-limit circuitry is increased effective to enable the switching regulator to draw an amount of input current that exceeds the predefined current limit. The switching regulator is then permitted to operate with the increased current limit for a predetermined number of cycles, which can be effective to enable the switching regulator to provide the current to the load more quickly.

RELATED APPLICATIONS

This present disclosure claims priority to U.S. Provisional PatentApplication Ser. No. 62/115,058 filed Feb. 11, 2015, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Unless otherwiseindicated herein, the approaches described in this section are not priorart to the claims in this disclosure and are not admitted to be priorart by inclusion in this section.

Computing and electronic devices include power regulators for steppingbattery or external power down to voltages that are suitable for variousinternal components, such as processors, memory, displays, networkinterfaces, and the like. Efficiency of power regulation is often animportant performance metric because inefficient power regulatorsproduce excessive heat, consume more design space, or reduce run-timesof battery-powered devices. To optimize power regulator efficiency,power regulators typically implement multiple operating modes thatprovide optimal efficiencies over different respective ranges of currentloading.

Current loads of many device components (e.g., processors), however, aredynamic and can quickly transition from very low current loads to veryhigh current loads. When these load transitions occur, power regulatorsoften switch between operating modes to accommodate the increased amountof current drawn by the components. In some cases, latency associatedwith switching between the operating modes allows the increased amountof current to draw down a voltage of the power regulator's output. Ifthe voltage at the regulator's output falls below a minimumspecification for the components, the components of the device can beimpaired or damaged by operating in a low-voltage condition.

SUMMARY

This summary is provided to introduce subject matter that is furtherdescribed below in the Detailed Description and Drawings. Accordingly,this Summary should not be considered to describe essential features norused to limit the scope of the claimed subject matter.

A method is described for detecting that a switching regulator istransitioning to a continuous mode of operation to provide current to aload connected to an output of the switching power regulator. Inresponse to the transition to the continuous mode of operation, apredefined current limit of the switching regulator's current-limitcircuitry is increased effective to enable the switching regulator todraw an amount of input current that exceeds the predefined currentlimit. The switching regulator is then permitted to operate with theincreased current limit for a predetermined number of operating cycle,which can be effective to provide the current to the load more quickly.

A power supply circuit is described that includes a transistorconfigured to provide current to a load connected to an output of thepower supply circuit and current-limit circuitry configured to limit,based on a predefined current limit, an amount of input current drawn bythe transistor. A controller of the circuit is configured to transitionto a continuous mode operation to provide an increased amount of currentto the load. In response to transitioning to the continuous mode ofoperation, the controller increases a predefined current limit of thecurrent-limit circuitry effective to enable the transistor to draw anamount of input current that exceeds the predefined current limit. Thepower supply circuit is then permitted to operate with the increasedcurrent limit for a predetermined number of operating cycles. By sodoing, the transistor can provide the increased amount of current to theload more quickly.

A System-on-Chip (SoC) is described that includes first and secondtransistors coupled to an output of the SoC at which current is providedby the first and second transistors to power a load. The SoC alsoincludes current-limit circuitry that is configured to limit, based on apredefined current limit, an amount of input current drawn by the firsttransistor. A controller of the SoC is configured to transition from adiscontinuous mode of operation to a continuous mode operation toprovide an increased amount of current to the load. In response totransitioning to the continuous mode of operation, the controllerincreases the predefined current limit of the current-limit circuitryeffective to enable the transistor to draw an amount of input currentthat exceeds the predefined current limit. The SoC is then permitted tooperate with the increased current limit for a predetermined number ofoperating cycles effective to enable the transistor to provide theincreased amount of current to the load more quickly.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations of fast transient responsefor switching regulators are set forth in the accompanying figures andthe detailed description below. In the figures, the left-most digit of areference number identifies the figure in which the reference numberfirst appears. The use of the same reference numbers in differentinstances in the description and the figures indicate like elements:

FIG. 1 illustrates an operating environment having computing devices andswitching regulators in accordance with one or more aspects.

FIG. 2 illustrates an example configuration of the switching regulatorsand device components shown in FIG. 1.

FIG. 3 illustrates an example switching regulator that includescircuitry for fast transient response in accordance with one or moreaspects.

FIG. 4 illustrates another example switching regulator that includescircuitry for fast transient response in accordance with one or moreaspects.

FIG. 5 illustrates an example method for connecting a transconductanceload to an error amplifier to increase a transconductance of the erroramplifier.

FIG. 6 illustrates an example method for isolating a compensationcapacitor.

FIG. 7 illustrates an example method for increasing a current limit of ahigh-side switching element.

FIG. 8 illustrates an example method for monitoring an output voltage ofa switching regulator for voltage drop.

FIG. 9 illustrates a System-on-Chip (SoC) environment for implementingaspects of fast transient response for switching regulators.

DETAILED DESCRIPTION

Conventional switching regulators typically operate in different modesto regulate power efficiently over different respective ranges ofcurrent loading. For example, a switching regulator may operate in acontinuous mode (e.g., pulse-width modulation) to provide a high amountof current or a discontinuous operating mode (e.g., pulse frequencymodulation mode) to conserve power while providing a small amount ofcurrent. While operating in either mode, however, conventional switchingregulators use similar feedback or compensation circuitry to controlcharacteristics of the power provided by the switching regulator. Thiscan be problematic when load steps occur, such as when a processor wakesup from a sleep state and load demand on the switching regulator rapidlytransitions from a few micro amps (or micro amperes) to multiple amps(or amperes).

While operating in the discontinuous mode, there are long periods oftime for which the switching regulator is inactive. During these periodsof time, the feedback or compensation circuitry can discharge orsaturate down to low voltage levels, which slows the switchingregulator's response for regulating voltage. For low current loads, thisis acceptable because a bulk capacitance at the switching regulator'soutput is often able to provide a few micro amps to a few milliamps ofcurrent while the feedback circuitry recovers. For a load step to highcurrent load, however, the bulk capacitance is relatively small and thehigh current load can quickly draw down voltage at the switchingregulators output.

For example, consider feedback circuitry that includes an erroramplifier (e.g., feedback amplifier) with an output of one microamp anda compensation capacitor of ten picofarads, which would take 1microsecond to charge at one microamp. A load step of one amp applied toa switching regulator with ten microfarad of bulk output capacitance forone microsecond can drop the output voltage by more than 100 millivolts.For processors fabricated on advanced technologies (e.g., 28 nm or 16nm) that operate at one volt or less, 20 mV, 30 mV, or 100 mVconstitutes an appreciable percentage of nominal supply voltage. Asnoted above, operating processors or other components in low-voltageconditions can compromise performance, integrity, or structure of thesecomponents.

This disclosure describes apparatuses and techniques of fast transientresponse for switching regulators. In some aspects, a transconductanceload is connected to an output of an error amplifier of a switchingregulator that is operating in a discontinuous mode. This can beeffective to dampen an indication of voltage at the switchingregulator's output and prevent the output of the error amplifier fromsaturating down to a low-voltage. By so doing, the switching regulatorcan more-quickly respond, based on the dampened indication of thevoltage, to a load's increased demand for current, thereby improving atransient load response of the switching regulator. In at least somecases, improving the switching regulator's transient response reducesvoltage drop at the regulator's output when load steps occur. Reducingor eliminating the voltage drop can ensure proper component operation orprevent damage associated with operating components in low-voltageconditions. Alternately or additionally, after transitioning from thediscontinuous mode to a continuous mode, a current limit of theswitching regulator can be allowed to exceed its nominal current limitprotection threshold (e.g., a peak current limit) by a predefined amountof current, for a predetermined amount of time, or for a predefinednumber of switching cycles.

The following discussion describes an operating environment, techniquesthat may be employed in the operating environment, and a System-on-Chip(SoC) in which components of the operating environment can be embodied.In the discussion below, reference is made to the operating environmentby way of example only.

Operating Environment

FIG. 1 illustrates an example operating environment 100 having acomputing device 102, which is capable of operating by drawing powerfrom a battery or an external source. Examples of the computing device102 include a smart phone 104, a tablet computer 106, a laptop computer108, a broadband router 110, and a digital camera 112. Further examplesof the computing device 102 include a desktop computer, a set-top-box, adata storage appliance (e.g., network-attached storage), a personalmedia device, a navigation device, a portable gaming device, and so on.The computing device 102 may draw the operating power for any suitablepurpose, such as to enable functionalities of a particular type ofdevice, provide a user interface, enable network access, implementgaming applications, capture images, play media, edit content, and thelike.

The computing device 102 includes processors 114 and computer-readablestorage media 116. The processors 114 can be any suitable type ofprocessor, either single-core or multi-core, for executing code,instructions, or commands of an operating system or application of thecomputing device 102. The computer-readable media 116 (CRM 116) mayinclude volatile memory or nonvolatile memory to store device data 118.In the context of this disclosure, the CRM 116 is implemented as storagemedia, and thus does not include transitory signals or carrier waves.

The computing device 102 may also include input/output (I/O) ports 120,a display 122, and data interfaces 124. The I/O ports 120 allow acomputing device 102 to interact with other devices and/or users. TheI/O ports 120 may support a variety of connections, such as a universalserial bus (USB), peripheral component interconnect express (PCIe) port,serial port, parallel port, or infrared port. The display 122 presentsgraphics of the computing device 102, which may include user interfaceelements of an operating system, applications, or system utilities.

The data interfaces 124 provide connectivity to one or more networks andother devices connected therewith. The data interfaces 124 may includewired interfaces, such as Ethernet or fiber optic interfaces forcommunicating over a local network, intranet, or the Internet. In somecases, the data interfaces 128 include wireless interfaces thatfacilitate communication over wireless networks, such as wirelesslocal-area-networks (WLANs), cellular networks, and/or wirelesspersonal-area-networks (WPANs).

The computing device 102 may also include a battery 126 that providespower to support operations of the device's components, such as theprocessors 114, display 122, or data interfaces 124. Although not shown,the computing device 102 includes an external power connection throughwhich power is received to charge the battery 126. In some cases, theexternal power connection is implemented in conjunction with one of thedata interfaces 124, such as a USB port. Alternately or additionally,the components of the computing device 102 may operate from the powerreceived via the external power connection while the battery 126 ischarged.

A power system 128 of the computing device 102 steps power from thebattery 126 down to voltages that are suitable for use by the device'scomponents. The power system 128 includes switching regulators 130 andtransient response circuitry 132 (response circuitry 132). Although notshown, power system 130 may also include a charging circuit capable ofcharging battery 126 using an external power source (e.g. an alternatingcurrent (AC) or direct current (DC) source). The switching regulators130 may include any suitable number of regulators configured to providepower at various voltages, such as five volts, three volts, one volt,and so on. The implementation and use of response circuitry 132 varies,and is described below.

FIG. 2 illustrates an example configuration of the power system 128 andswitching regulators 130 of FIG. 1 generally at 200. In this particularexample, the power system 130 includes a 1.0 volt switching regulator202 (1.0 V regulator 202), a 1.8 volt switching regulator 204 (1.8 Vregulator 204), and a 3.3/5.0 volt switching regulator 206 (3.3/5.0 Vregulator 206), which is configured as a dual output switchingregulator. Each of the power regulators 202, 204, and 206 also include arespective instance of response circuitry 132, the implementation anduse of which is described below. The switching regulators of powersystem 130 step down voltage of the power provided by the battery 126 oran external power source 208 of computing device 102, such as an ACadapter.

Each component of the computing device 102 may operate at differentnominal voltage, such as 5.0 volts, 3.3 volts, 1.8 volts, 1.0 volt, 0.9volts, and so on. As shown in FIG. 2, the 1.0 volt regulator 202 stepsdown battery or external power to 1.0 volt for one of processors 114,which is configured as an application processor 210. The applicationprocessor 210, or others of the processors 114, may have multipleoperating states, such as full-power, half-power (e.g., half ofprocessing cores active), idle, sleep, off, and the like. Operationalpower, and thus current, consumed by the application processor 210 ineach of the operational states may also vary. For example, theapplication processor 210 may consume a few micro amps while in a sleepstate, a few milliamps while idle, and multiple amps in a full-poweroperational state. As such, a load step associated with waking theapplication processor 210 from a sleep state may include a current drawtransition from a few micro amps to multiple amps (e.g., five to sixamps).

The 1.8 volt regulator 204 steps down battery or external power to 1.8volts for another of processors 114, which is configured as a graphicsprocessor 212. The graphics processor 212 may also have multipleoperating states ranging from full-power to off and consume variousamounts of operating current, ranging from a few milliamps to multipleamps. In some cases, waking the graphics processor 212 from an idle orsleep state subjects the 1.8 volt regulator to a load step of multipleamps. The 1.8 volt regulator also provides operating power at 1.8 voltsfor dynamic random access memory (DRAM) 214, flash memory 216, and othercomponents having an operating voltage of 1.8 volts.

The 3.3/5.0 volt regulator 206 steps down battery or external power to3.3 volts and 5.0 volts for the I/O ports 120, display 122, and one ofthe data interfaces 124, which is configured as a wireless modem 218.Any or all of these components may have multiple operating states andmay be powered down to lower operational state when possible to conservepower of the battery 126. For example, a power management utility of thecomputing device 102 may power down the processors 114, DRAM 214,display 122, and wireless modem 218 after a predetermined amount of timeelapses for which the computing device 102 is inactive (e.g., devicesleep state).

FIG. 3 illustrates an example of a switching regulator 300 that includescircuitry for fast transient response in accordance with one or moreaspects. The switching regulator 300 is configured to step power (e.g.,battery power) from an input power rail or input voltage 302 (V_(IN)302) down to an output voltage 304 (V_(OUT) 304), which is suitable foruse by a load 306. Examples of the load 306 may include the processors114, CRM 116, display 122, data interfaces 126, or other components ofthe computing device 102.

The switching regulator 300 includes a high-side switch 308 connected toV_(IN) 302 and low-side switch 310 connected to ground (e.g., a groundrail or other lower potential) that provide current to the load 306 viaan external inductor 312 (L_(EXT) 312). The high-side switch 308 andlow-side switch 310 may be implemented using any suitable transistors,such as n-channel and p-channel metal-oxide-semiconductor field-effecttransistors (MOSFETs). Although shown as internal components of theswitching regulator 300, the high-side switch 308 and low-side switch310 may be implemented as external discrete components.

The external inductor 312 and external capacitor 314 store energy at theoutput of the switching regulator 300. For example, while the high-sideswitch 308 is active current in the external inductor 312 and voltage inthe external capacitor 314 ramp up. When the high-side switch 308 isoff, the energy stored by the external inductor 312 and externalcapacitor 314 is released to the load 306. These components function asan inductor-capacitor (LC) low-pass filter that smooths the output ofpower provided by the switching regulator 300.

The high-side switch 308 and low-side switch 310 are controlled byswitching controller 316, which may be implemented as any suitable typeof microcontroller, state machine, digital-signal processor (DSP) andthe like. The switching controller 316 activates or turns on thehigh-side switch 308 or low-side switch 310 to regulate the outputvoltage 304. Alternately or additionally, the switching controller 316may also control the high-side switch 308 or low-side switch 310 toregulate an amount of current or power provided to the load 306.

To regulate the output voltage 304 of the switching regulator 300, theswitching controller 316 receives feedback of current or voltageprovided at the output of the switching regulator 300. For example, acurrent-to-voltage converter 318 provides an indication of switchcurrent provided by the high-side switch 308 or low-side switch 310. Theoutput voltage 304 is reduced to an acceptable signal level by aresistor network 320 (R_(NET) 320) or voltage divider and then amplifiedby an error amplifier 322 based on a reference voltage 324 (V_(REF)324). An indication of the output voltage 304 is provided by an outputof the error amplifier 322, which is compensated by high frequencycompensation capacitor 326, compensation resistor 328, and compensationcapacitor 330.

A comparator 332 receives the indication of the switch current and theindication of the output voltage 304 at respective inputs and provides acomparison result to the switching controller 316. Based on thiscomparison result of the feedback, the switching controller 316 canactivate the high-side switch 308 or low-side switch 310 to regulate theoutput voltage 304. In some cases, the switching controller 316 operatesin a continuous mode or frequency-based modes, such as a constantfrequency mode or pulse-width modulation (PWM) mode. In a continuousmode, the switching controller 316 can activate the high-side switch 308and low-side switch 310 based on an approximate operating frequency thatranges from 500 KHz to several mega-Hertz (e.g., 0.5-7 MHz). Thecontinuous mode of the switching regulator may efficiently provide powerfor high-current loads (e.g., multiple amps), such as processors orwireless modems operating at full-power.

The switching regulator 300 also operates in a discontinuous mode, suchas a power save mode (PSM) or pulse frequency modulation (PFM) mode. Inthe discontinuous mode, the switching regulator 300 may wait until theoutput voltage 304 falls below a threshold before turning on high-sideswitch 308. For example, the output voltage 304 may saw-tooth between amaximum PFM mode voltage and the threshold while the load 306 continuesto draw current. In other words, an operational frequency of theswitching regulator 300 or high-side switch 308 may be non-constant,variable, or adjusted based on an indication of the voltage at theoutput of switching regulator 300.

The discontinuous mode or PFM mode may efficiently provide power forlow-current loads (e.g., microamps or milliamps), such as processors orwireless modems in an idle or sleep state. In some cases, whileoperating in the PFM mode, the switching regulator 300 only switches onwhen more power is needed. In other words, most of the time theswitching regulator 300 is in an off-state that consumes no power (e.g.,no power loss). Therefore, the power loss is significantly reduced inthe PFM mode, which increases an efficiency of the switching regulator300 with light load conditions.

In some aspects, the response circuitry 132 includes a transconductanceload 334 and a switch 336, which is useful to connect thetransconductance load 334 to the output of error amplifier 322. In thisparticular example, the transconductance load 334 is configured as anoperational amplifier (op-amp) buffer (e.g., unity gain buffer) with aninput set by low-power feedback voltage 338 (V_(FB) _(_) _(LP) 338). Thelow-power feedback voltage 338 can be set to an approximate nominalvoltage of the error amplifier 322 effective to prevent the output ofthe error amplifier from saturating when the transconductance load isconnected thereto.

Transconductance load 334 may have any suitable transconductance (gm),such as a transconductance proportional to or less than atransconductance of the error amplifier 322. In some cases, thetransconductance load 334 has a transconductance value that ranges fromapproximately one half to one quarter of that of the error amplifier322. In other cases, the transconductance load 334 has atransconductance that is less than approximately one quarter of thetransconductance of the error amplifier 322. These transconductance loadvalues can be effective to decrease a DC gain from the input of theerror amplifier 322 when the transconductance load 334 is connected tothe output of the error amplifier.

For example, when the transconductance load 334 is approximately onefourth of the transconductance of the error amplifier 322, the DC gainof the error amplifier is approximately four (e.g., gm/(gm/4)=4).Alternately or additionally, connecting the transconductance load 334 tothe output of the error amplifier 322 converts the error amplifier 322from an integrator to a damped integrator with an output gain that isinversely proportional to the value of the transconductance load 334(e.g., a gain of 4). In some cases, this can be effective to prevent theoutput of the error amplifier 322 from saturating to a low-voltage levelduring periods of inactivity, such as when the switching regulator 300operates in a discontinuous mode, pulse frequency modulation mode, orpower save mode.

In other aspects, the response circuitry 132 includes a switch 340 todisconnect the compensation capacitor 330 from the output of the erroramplifier 322. The switch 340 may be located in any suitable location,such as between the resistor 328 and compensation capacitor 330 orbetween the output of the error amplifier 322 and the resistor 328. Insome cases, disconnecting the compensation capacitor 330 prevents thecompensation capacitor 330 from discharging during periods ofinactivity, such as when the switching regulator 300 operates in adiscontinuous mode or PFM mode. Because the output of the erroramplifier 322 may be limited to a few microamps, disconnecting thecompensation capacitor 330 can be effective to reduce an amount ofenergy, and therefore time, the compensation capacitor 330 consumes tocharge up to a nominal operating voltage. For example, reconnecting anon-discharged compensation capacitor 330 when transitioning to acontinuous operation mode can enable the switching regulator 300 torespond more-quickly to load steps.

The response circuitry 132 may also include a switch 342 to connect thecompensation capacitor 330 to an op-amp buffer 344 that is configured toprovide charging energy. In some cases, the compensation capacitor 330is connected to the op-amp buffer 344 while the compensation capacitor330 is disconnected from the output of the error amplifier 322.Connecting the compensation capacitor 330 to the op-amp buffer 344enables the compensation capacitor to be at least partially charged orpre-charged while out-of-circuit. For example, when the switchingregulator 300 operates in a discontinuous mode or PFM mode, thecompensation capacitor 330 can be pre-charged based on an input voltageof the op-amp buffer 344. The input voltage of the op-amp buffer 344 canbe any suitable voltage, such as the low-power feedback voltage 338. Inthis particular example, an offset voltage 346 of approximately 25millivolts is applied to the low-power feedback voltage 338. As notedabove, reducing the energy consumed by the compensation capacitor tocharge up to a nominal voltage can enable the switching regulator 300 torespond more-quickly to load steps.

FIG. 4 illustrates another example of the switching regulator 300 thatincludes circuitry for fast transient response in accordance with one ormore aspects. In this particular example, the switching regulator 300includes a high-side current limiter 400 (H.S. I-limit 400) and alow-side current limiter 402 (L.S. I-limit 402). The high-side currentlimiter 400 and low-side current limiter 402 may be implemented as anysuitable type of circuitry, such as current sense resistors, resistornetworks, comparators, analog-to-digital converters, logic gates, and soon.

The high-side current limiter 400 and low-side current limiter 402monitor the switch current provided to the external inductor 312. Insome cases, the current limiters are configured with predefinedthresholds (e.g., time or amps) at which the high-side switch 308 andlow-side switch 310 are turned off to protect the switches or downstreamcomponents. For example, when the high-side switch 308 turns on, thehigh-side current limiter 400 monitors the current provided to theexternal inductor 312.

Responsive to the monitored current exceeding the predefined threshold(e.g., triggering a current limit), the high-side current limiter canprovide an indication of the excessive current to the switchingcontroller 316. To protect the high-side switch 308 or other components,the switching controller 316 can deactivate or turn off the high-sideswitch 308. When these current limits are triggered by a load step,deactivating the high-side switch 308 may prevent the switchingregulator 300 from being able to quickly respond to the load step. Inother cases, however, the switching controller 316 may allow the currentto exceed the predefined thresholds for a predefined number of switchingcycles to provide an increased amount of current to the load 306. Insuch cases, this increased amount of current may prevent voltage drop atthe output of the switching regulator 300, thereby improving theswitching regulator's response to a load step.

In other aspects, the response circuitry 132 includes comparator 404 aspart of an output voltage monitoring circuit. The output voltagemonitoring circuit may also comprise a reference output voltage 406(e.g., a specified output voltage 304) and voltage offset 408 thatenable calibration of the output voltage monitoring circuit. Thecomparator may directly monitor the voltage at the output of theswitching regulator and provide an indication of low output voltage tothe switching controller 316.

In some cases, a detection threshold provided by the reference outputvoltage 406 or the voltage offset 408 is set within an approximatevariation tolerance of the switching controller 316's regulation loop.In such cases, the voltage offset 408 may comprise approximately two tofive percent of the output voltage, which is subtracted from thereference output voltage 406 to provide a comparison threshold. Theswitching controller 316 may then receive an indication of low outputvoltage if the output voltage 304 falls, based on the voltage offset408, out of regulation for a given operational mode. Alternately oradditionally, the voltage offset 408 may be auto-calibrated when theswitching regulator starts to ensure accuracy of the voltage offset 408and associated comparison threshold for low-voltage monitoring. Further,the error amplifier 322 may also be trimmed or calibrated to reduce anoffset for accurate regulation of the output voltage or for generatingthe voltage offset 408 with a high accuracy.

Techniques of Fast Transient Response for Switching Regulators

The following discussion describes techniques of fast transient responsefor switching regulators. These techniques can be implemented using thepreviously described environments and entities, such as responsecircuitry 132 and various components thereof. These techniques includemethods illustrated in FIGS. 5, 6, 7, and 8, each of which is shown as aset of operations performed by one or more entities. These methods arenot necessarily limited to the orders shown for performing theoperations and may be looped, repeated, or re-ordered to implementvarious aspects described herein. Further, these methods may be used inconjunction with one another, in whole or in part, whether performed bythe same entity, separate entities, or any combination thereof. Inportions of the following discussion, reference will be made tooperating environment 100 of FIG. 1 and entities of FIGS. 3 and 4 by wayof example. Such reference is not to be taken as limited to operatingenvironment 100 but rather as illustrative of one of a variety ofexamples.

FIG. 5 depicts a method 500 for connecting a transconductance load to anerror amplifier to increase a transconductance of the error amplifier,including operations performed by the switching controller 316 and/orthe response circuitry 132.

At 502, it is determined that a switching regulator is operating in adiscontinuous mode to provide current to a load. The discontinuous modeof operation may include a pulse frequency modulation or power save modethat includes long periods of inactivity. In some cases, this inactivitypermits voltage of switching regulator's compensation circuitry todischarge or fall. For example, longer cycles of voltage feedback (e.g.,voltage saw-toothing) may cause an output of an error amplifier to drivedown the voltage of the compensation circuitry.

At 504, a transconductance load is connected to an output of theswitching regulator's error amplifier. This can be effective to dampenthe output of the error amplifier or reduce a DC gain of the erroramplifier. The transconductance load can be connected via any suitablemeans, such as a switch controlled by a controller of the switchingregulator. In some cases, connecting the transconductance load changesthe error amplifier from an integrator to a damped integrator with again proportional to the transconductance of the transconductance load.By so doing, voltage drop at the error amplifier's output can be limitedbased on the DC gain of the error amplifier.

At 506, an increase in the amount of current drawn by the load isdetected based on the damped output of the error amplifier. The amountof current drawn by the load may exceed the amount of current theswitching regulator provides in the discontinuous mode of operation. Forexample, the increase in the amount of current drawn may be a load stepof several amps, such as from microamps to several amps. In such cases,the load step may begin to draw down the voltage at the output of theswitching regulator. By limiting the error amplifier's output droop inthe discontinuous mode, the switching regulator is able to respondmore-quickly to the falling output voltage.

At 508, the switching regulator is transitioned from the discontinuousmode to a continuous mode of operation. In some cases, the transition tothe continuous mode of operation can be responsive to detecting theexcessive current draw of the load. In other cases, the transition canbe caused responsive to detecting that the amount of current consumed bythe load exceeds the amount of current being provided by the switchingregulator. Transitioning to the continuous mode of operation enables theswitching regulator to increase the amount provided to the load and thusprevent further loss of voltage at the switching regulator's output. Assuch, quickly responding to the load step can be effective to preventvoltage drop at the output of the switching regulator.

At 510, the transconductance load is disconnected from the output of theerror amplifier to cease the dampening of the output. This can beeffective to cease to dampen the output of the error amplifier, improvevoltage regulation at the output of the switching regulator, or tochange the error amplifier's function from a damped integrator to alossless integrator. The transconductance load can be disconnected viaany suitable means, such as by opening a switch controlled by acontroller of the switching regulator. In some cases, disconnecting thetransconductance load changes the error amplifier from a dampedintegrator with a gain to an integrator for operation in the continuousmode. From operation 510, the method may return to operation 502responsive to transitioning back to the discontinuous mode.

FIG. 6 depicts a method 600 for isolating a compensation capacitor,including operations performed by the switching controller 316 and/orthe response circuitry 132.

At 602, it is determined that a switching regulator is operating in adiscontinuous mode. In some cases, a transition into the discontinuousmode of operation is detected or caused, such as by a controller of theswitching regulator. The discontinuous mode of operation may include apulse frequency modulation mode that includes long periods ofinactivity. In some cases, the inactivity permits voltage of switchingregulator's compensation circuitry to discharge or fall. Alternately oradditionally, an error amplifier may drive a voltage of the compensationcircuitry low due to longer cycles of voltage feedback (e.g., voltagesaw-toothing) during which the output voltage remains above a feedbackthreshold of the discontinuous mode.

At 604, a capacitor is disconnected from a compensation circuit of theswitching regulator's error amplifier. The capacitor may be disconnectedvia any suitable means, such as a switch controlled by a controller ofthe switching regulator. In some cases, the capacitor is disconnectedresponsive to determining that the switching regulator is operating in adiscontinuous mode or detecting the transition into the discontinuousmode. Disconnecting the capacitor can be effective to prevent a voltagelevel of the capacitor from discharging or falling during inactive timesof the discontinuous mode. For example, while the output of theswitching regulator is higher than a reference voltage, the output ofthe error amplifier can be driven low for an extended amount of time. Insuch cases, disconnecting capacitor can prevent the error amplifier fromdriving down a voltage of the capacitor during this extended amount oftime.

Optionally at 606, the capacitor is charged to approximately a nominalvoltage of the compensation circuit. The capacitor may be connected to acharging source via another switch controlled by the controller of theswitching regulator. In some cases, the capacitor is charged by anop-amp, buffer amplifier, or voltage source configured to provide powerat a nominal voltage of the error amplifier's output. Alternately oradditionally, the charging source may be configured to provide power atan increased voltage level, such as 25 millivolts above the nominalvoltage of the error amplifier's output.

At 608, it is determined that the switching regulator is transitioningfrom the discontinuous mode to a continuous mode of operation. In somecases, the switching regulator transitions to the continuous mode ofoperation to respond a load step to an amount of current that is higherthan the current provided by the switching regulator in thediscontinuous mode. For example, an amount of current consumed by aprocessor waking from a sleep state to a full-power state may step orincrease from a few microamps to multiple amps of current.

At 610, the capacitor is connected to the compensation circuit of theerror amplifier. This can be effective to assist with (e.g., accelerate)charging the compensation circuit or returning the error amplifier'soutput to a nominal voltage. Because voltage of the capacitor was notdischarged while the switching regulator operated in the discontinuousmode, less energy is needed to bring the error amplifier's output to thenominal voltage. In cases in which the capacitor is charged at operation606, the error amplifier's output voltage may recover even more-quickly.By facilitating rapid charging of the compensation circuitry connectedto the error amplifier's output, the switching regulator is able toprovide current more-quickly in the continuous mode of operation. Thiscan be effective to enable the switching regulator to better respond toload steps that would otherwise draw down voltage at the switchingregulator's output.

FIG. 7 depicts a method 700 for increasing a current limit of ahigh-side switching element, including operations performed by theswitching controller 316 and/or the response circuitry 132.

At 702, it is determined that a switching regulator is transitioning toa continuous mode of operation. The switching regulator may transitionfrom an off state, sleep state, or from another mode of operation, suchas a discontinuous mode of operation. The continuous mode of operationmay be a PWM mode of the switching regulator that enables the switchingregulator to provide an increased amount of current to a load. In somecases, the transition to the continuous mode of operation is responsiveto sensing an increased amount of current drawn responsive to a loadstep. For example, a processor or wireless modem exiting a sleep statemay produce a load step of a few microamps to multiple amps of current,which begins to draw down the output voltage of the switching regulator.

At 704, a current limit of the switching regulator's high-side switch isincreased. This can be responsive to detecting that the switchingregulator is transitioning to the continuous mode of operation. Thecurrent limit that is increased may be any suitable type of currentlimit, such as an amount of current, a number of cycles the regulatoroperates while the current exceeds the current limit, or an amount oftime that the current is permitted to exceed the current limit. Forexample, an amount of time (or current) that the current is allowed toexceed a predefined current limit (e.g., eight amps) may be increasedapproximately 25-30%. By so doing, the high-side switch can deliver anincreased amount of current to the load at the switching regulator'soutput. Alternately or additionally, a current limit for the switchingregulator's low-side switch can be increased to provide similar results.

At 706, the switching regulator is permitted to operate with theincreased current limit. The switching regulator may operate with theincreased current limit for any suitable amount of time or number ofoperating cycles. As described above, the switching regulator may bepermitted to operate for approximately 25-30% higher than typicallypermitted before limiting current provided by the high-side switch. Insome cases, the switching regulator operates with the increased currentlimit for the first few PWM cycles (e.g., two to ten cycles) after thetransition. In other cases, the switching regulator operates with theincreased current limit for a particular amount of time, such as one toten microseconds. Accordingly, the switching regulator is able todeliver or provide the increased amount of current for at least a shortduration of time, which enables the switching regulator to more-quicklyrespond to load steps.

At 708, the current limit of the switching regulator's high-side switchis restored. In some cases, this is effective to prevent high levels ofcurrent from damaging components of the switching regulator, such as theswitching transistors or external inductor. The current limit can berestored for subsequent operation in the continuous mode or until theswitching regulator transitions to another operating mode. In somecases, this can be effective to preclude operation 702 because thecurrent limit is modified prior to transitioning to the continuous mode.

FIG. 8 depicts a method 800 for monitoring an output voltage of aswitching regulator for voltage drop, including operations performed bythe switching controller 316 and/or the response circuitry 132.

At 802, an output voltage of a switching regulator is directly monitoredwhile the switching regulator operates in a discontinuous mode. Thediscontinuous mode of operation may include a pulse frequency modulationmode or power save mode. In some cases, the output voltage is monitoredby a comparator having an input connected to the switching regulator'soutput and an output connected to a controller of the switchingregulator. The switching regulator may include another comparator orerror amplifier that provide an indication of the output voltage duringoperation in a continuous mode.

At 804, a high-side switch of the switching regulator is turned onresponsive to the output voltage falling below a predefined threshold.For example, an increased amount of current draw caused by a load stepmay cause the output voltage of the switching regulator to fall belowthe predefined threshold. The predefined threshold may be set atapproximately a specified output voltage for the switching regulator,such as approximately two to five percent of the specified outputvoltage. In some cases, the predefined threshold is calibrated duringstartup of the switching regulator to ensure an accuracy of thepredefined threshold. For example, after measuring the output voltage ofthe switching regulator in either mode of operation, the predefinedthreshold can be set for two percent below a nominal output voltage ofthe switching regulator.

At 806, the switching regulator is transitioned from the discontinuousmode to a continuous mode in response to the output voltage fallingbelow the predefined threshold. During this transition, the top-sideswitch 308 may also be activated to charge the external inductor 304 toprovide current to the external capacitor 314 and the load 306. Theswitching regulator then controls, via the continuous mode, subsequentoperation of the high-side switch. This can be effective to enable theswitching regulator to provide an increased amount of current to respondto a load step. In at least some cases, the direct monitoring of theoutput voltage and comparison with the predefined threshold enables theswitching regulator to transition to the continuous mode more-quicklythan a conventional feedback loop. By so doing, current is providedmore-quickly in response to the load step thereby reducing a voltagedrop at the output of the switching regulator.

System-on-Chip

FIG. 9 illustrates a System-on-Chip (SoC) 900, which can implementvarious aspects of fast transient response for switching regulators. ASoC can be implemented in any suitable device, such as a smart-phone, acellular phone, a laptop computer, a tablet computer, a server, awireless router, network-attached storage, a camera, or any other typeof device that may implement arrayed memory.

The SoC 900 can be integrated with electronic circuitry, amicroprocessor, memory, input-output (I/O) logic control,analog-to-digital circuits, communication interfaces and components,other hardware, firmware, and/or software useful to provide powermanagement for a device, such as any of the above-listed devices. SoC900 can also include an integrated data bus (not shown) that couples thevarious components of the SoC for data communication between thecomponents. In some cases, these various components may be configured toimplement concepts described herein via internal components (e.g.,transistors), external components (e.g., inductors or capacitors), orany suitable combination thereof.

In this example, the SoC 900 includes various components such asinput-output (I/O) logic control 902 (e.g., analog-to-digital ordigital-to-analog logic) and a microprocessor 904 (e.g., any of amicrocontroller, application processor, DSP, or PWM controller). The SoC900 also includes a memory 906, which can be any type of RAM,nonvolatile memory (e.g., NAND Flash), read-only memory (ROM),electronically erasable programmable ROM (EEPROM), and/or other suitableelectronic data storage. The SoC 900 can also include various statemachines, software, or operating systems, such as firmware 908, whichcan be processor-executable instructions maintained by memory 906 andexecuted by microprocessor 904. The SoC 900 can also include othervarious communication interfaces and components, other hardware,firmware, and/or software.

The SoC 900 also includes switch FETs 910, compensation circuitry 912(e.g., resistors and capacitors), a switching controller 316, andresponse circuitry 132, which may be embodied as disparate or combinedcomponents, as described in relation to aspects presented herein.Examples of these various components, functions, and/or entities, andtheir corresponding functionality, are described with reference to therespective components of the environment 100 shown in FIGS. 1, 3, and 4.The switching controller 316, either in whole or part, can beimplemented as processor-executable instructions maintained by thememory 906 and executed by the microprocessor 904 to implement variousaspects and/or features described herein. In some cases, the SoC 900 isimplanted as a switch-mode power supply (SMPS) controller or powermanagement integrated circuit (PMIC).

The switching controller 316 and response circuitry 132, eitherindependently or in combination with other entities, can be implementedwith any suitable combination of components to implement various aspectsand/or features described herein. Response circuitry 132 may also beprovided integral with other entities of SoC 900, such as integratedwith the I/O logic 902, compensation circuitry 912, or any other signalprocessing or conditioning section within SoC 900. Alternately oradditionally, the response circuitry 132 and the other components can beimplemented as hardware, firmware, fixed logic circuitry, or anycombination thereof that is implemented in connection with powermanagement circuitry of the computing device 102.

Although the subject matter has been described in language specific tostructural features and/or methodological operations, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or operations describedabove, including orders in which they are performed.

What is claimed is:
 1. A method comprising: detecting that a switchingregulator is transitioning to a continuous mode of operation to providecurrent to a load connected to an output of the switching regulator, thecurrent provided by a transistor of the switching regulator that isoperably connected between a power source and the load; increasing, inresponse to the transition to the continuous mode of operation, apredefined current limit of current-limit circuitry interposed betweenthe power source and the transistor effective to enable the transistorto draw an amount of input current that exceeds the predefined currentlimit; and permitting, for a predetermined number of operating cycles,the switching regulator to operate with the increased current limiteffective to provide, via the transistor, the current to the load morequickly.
 2. The method as recited in claim 1, wherein the switchingregulator is transitioning to the continuous mode of operation from adiscontinuous mode of operation.
 3. The method as recited in claim 1,further comprising restoring, after the predetermined number ofoperating cycles, the predefined current limit of the current-limitcircuitry for subsequent operation in the continuous mode of operation.4. The method as recited in claim 1, wherein the predefined currentlimit of the current-limiting circuitry is increased by approximately 25to 30 percent.
 5. The method as recited in claim 1, wherein thepredetermined number of operating cycles ranges from two to tenoperating cycles.
 6. The method as recited in claim 1, whereinpermitting the switching regulator to operate for the predeterminednumber of operating cycles is effective to permit the switchingregulator to operate with the increased current limit for approximatelyone to ten microseconds.
 7. The method as recited in claim 2, whereinthe continuous mode of operation is a pulse-width modulation mode or thediscontinuous mode of operation is a pulse frequency modulation mode. 8.A power supply circuit comprising: a transistor coupled to a powersource and configured to provide current to a load connected to anoutput of the power supply circuit; current-limit circuitry interposedbetween the power source and the transistor configured to limit, basedon a predefined current limit, an amount of input current drawn by thetransistor; and a controller operably connected to the output of thepower supply circuit and to a gate of the transistor, the controllerconfigured to: control, via a discontinuous mode of operation and basedon a voltage at the output of the power supply circuit, an amount of thecurrent provided by the transistor to the load; transition from thediscontinuous mode of operation to a continuous mode operation toprovide an increased amount of current to the load; increase, inresponse to transitioning to the continuous mode of operation, thepredefined current limit of the current-limit circuitry effective toenable the transistor to draw an amount of input current that exceedsthe predefined current limit; and permit, for a predetermined number ofoperating cycles, the power supply circuit to operate with the increasedcurrent limit effective to enable the transistor to provide theincreased amount of current to the load more quickly.
 9. The powersupply circuit as recited in claim 8, wherein the controller is furtherconfigured to restore, after the predetermined number of operatingcycles, the predefined current limit of the current-limit circuitry forsubsequent operation in the continuous mode of operation.
 10. The powersupply circuit as recited in claim 8, wherein the predefined currentlimit of the current-limiting circuitry is increased by approximately 25to 30 percent.
 11. The power supply circuit as recited in claim 8,wherein the predetermined number of operating cycles ranges from two toten operating cycles.
 12. The power supply circuit as recited in claim8, wherein permitting the power supply circuit to operate for thepredetermined number of operating cycles is effective to permit thepower supply circuit to operate with the increased current limit forapproximately one to ten microseconds.
 13. The power supply circuit asrecited in claim 8, wherein the continuous mode of operation is apulse-width modulation mode or the discontinuous mode of operation is apulse frequency modulation mode.
 14. The power supply circuit as recitedin claim 8, wherein the transistor is a high-side transistor and thecurrent-limit circuitry is connected to a source of the high-sidetransistor.
 15. A System-on-Chip (SoC) comprising: a first transistorcoupled to a power rail of the SoC and an output of the SoC at whichcurrent is provided by the first transistor to power a load; a secondtransistor coupled to ground rail of the SoC and the output of the SoCat which the current is provided by the second transistor to power theload; current-limit circuitry interposed between the power rail and thefirst transistor that is configured to limit, based on a predefinedcurrent limit, an amount of input current drawn by the first transistor;and a controller operably connected to the load and respective gates ofthe first and second transistors, the controller configured to: control,via a discontinuous mode of operation and based on voltage of the powerprovided to the load, an amount of the current provided by the first andsecond transistors to the load; transition from the discontinuous modeof operation to a continuous mode operation to provide an increasedamount of current to the load; increase, in response to transitioning tothe continuous mode of operation, the predefined current limit of thecurrent-limit circuitry effective to enable the first transistor to drawan amount of input current that exceeds the predefined current limit;and permit, for a predetermined number of operating cycles, the SoC tooperate with the increased current limit effective to enable the firsttransistor to provide the increased amount of current to the load morequickly.
 16. The System-on-Chip of claim 15, wherein the controller isfurther configured to restore, after the predetermined number ofoperating cycles, the predefined current limit of the current-limitcircuitry for subsequent operation in the continuous mode of operation.17. The System-on-Chip of claim 15, wherein the predefined current limitof the current-limiting circuitry is increased by approximately 25 to 30percent.
 18. The System-on-Chip of claim 15, wherein the predeterminednumber of operating cycles ranges from two to ten operating cycles. 19.The System-on-Chip of claim 15, wherein the continuous mode of operationis a pulse-width modulation mode and the discontinuous mode of operationis a pulse frequency modulation mode.
 20. The System-on-Chip of claim15, wherein the SoC is implemented as a switch-mode power supplycontroller or power management integrated circuit.